Yes, you will need a visa if you get off the boat.
There are different cases though, and the UK government offers some questionnaire to help you.
You do not get off the boat
If you do not get off the boat, or to be precise if you do not cross the UK border control, then you do not need a visa, according to the UK government website.
You get off the boat, you stay in UK for less than 48 hours, your destination is not the UK
You a priori need only a Visitor in Transit Visa. On the page, it sounds like it is intended for air travel, but the wording lets think you would be eligible for that if you spend less than 48 hours in the UK, you have another destination and do NOT go to Ireland. But keep reading.
You get off the boat, you stay for more than 48 hours in the UK, or you go to Ireland too
You will need a visitor visa (if you follow the link, see point 3) if you stay for more than 48 hours in the UK or if you are "travelling to the Republic of Ireland, the Channel Islands or the Isle of Man". This is most likely your case.
I encourage you to read the question @DJClayworth linked on the topic. The recent changes (Dec. 2014) for Philippines citizens is that you need a transit visa when you transit landside between two flights, so that does not concern you.
I also encourage you to check the travel information page of your cruise, for example Norwegian cruises offer some very informative page (not dealing with the UK unfortunately).